Allow (c_names ...) in (executable ...)

[Niols]

Hello,

By discussing with @diml in #1832 (thanks again), I discovered the (modes object) stanza in order to build a C library from OCaml code super easily. However, in my case, we wrote a little piece of C wrapper around that library in order to have more C-like access points.

I think it would be nice to be able to declare this wrapper as C stubs in the (executable ...) stanza, that is to have (c_names ...) allowed in there (and probably (cxx_names ...) as well). Do you think it's reasonable?

[rgrinberg]

Would this proposal work for you?: #1786

You will be able to define an executable using pure C. Note that we'll still probably add support to {c,cxx}_names to the executable stanza.

[Niols]

In my case, it's indeed a pure C piece of code that depends on my OCaml library, but the goal is to build an object file and not an executable. However, as I guess it's very similar, could that be a feature in this PR?